Servo Speed Basic Stamp

mike1

Hello,

My daughter and I are working on building the Boe-Bot and we tested the servos motors.· The direction of the motors worked and the speeds of fast, medium and slow (based on the timing seem to work).· However, one servo seems to turn slightly faster than the other.· What would cause this odd behavior?

Thanks

Mike Green

This is normal behavior. Servos are normally designed to move to a specific position specified by the width of a control pulse repeated about every 20ms. This pulse is normally 1ms to 2ms in width. Some servos respond to a wider range of pulses, perhaps as much as 0.5ms to 2.5ms. The physical range of movement can also vary depending on the model and manufacturer and even between two of the same models. The continuous motion servos that are used in the Boe-Bot are modified standard servos with the position feedback disabled and the physical stop in the gears removed so the motor shafts can move through 360 degrees.

The way you adjust for the variation from servo to servo, is to change the values used in the PULSOUT statements. With the BS2, 750 corresponds to 1.5ms (2 microseconds per count). Typically, 650 may be used for rotation in one direction and 850 may be used for the other direction. In your case, use those values for one servo and try either 670 / 830 or 630 / 870 for the other. If that doesn't work, try other values. Make sure you've centered the servos (so they stop with a 750 value).

mike1

Thanks.· That is where I was headed it just surprized me that there was a difference in the·rotational·speeds of the two servo motors.